In long-distance transmission of optical signals, the accumulation of chromatic dispersion in optical fibers presents serious problems. These problems intensify with an increase in bit rate and the distance traveled by the optical signals. Efforts to date that compensate for dispersion have primarily involved the use of dispersion compensating optical fibers (DCF).
Dispersion compensating efforts that employ DCF—while well-proven—are not particularly amenable to integration in existing network elements. This is due—in part—because DCF is employed as a large spool of fiber which occupies significant space in a network office and is not adjustable. In addition, service providers that utilize DCF in their networks must accurately characterize their fiber, deploy more expensive optical amplifiers and accept additional latency added to links employing the DCF [˜20% additional latency for a fully compensated standard-single-mode fiber (SSMF) link]. Finally, DCF cannot satisfy all of the dispersion compensation requirements of many 40-Gb/s links, consequently a tunable optical dispersion compensator (TODC) having a small tuning range is often required in addition to the DCF.
A TODC employing an arrayed waveguide grating (AWG) and thermo-optic lens was described in U.S. Pat. No. 7,006,730 directed to a “Multichannel Integrated Tunable Thermo-Optic Lens and Dispersion Compensator the entire contents of which are hereby incorporated by reference. The TODC described therein appeared to be an attractive alternative/supplement to DCF.